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Mixon Hole Deep Water Gully

English Channel off Selsey Bill, West Sussex, England

Mixon Hole forms a 30 m deep underwater gully which was use by the Romans to transport goods.

The geology consists of limestone overlying grey clay and the Mixon Hole represents the north side of a drowned river gorge which is kept open by the strong tidal currents through it.

The north face of the hole is a clay cliff, vertical in its upper parts, from 5 -20 metres below sea level. At the top of the cliff there is an overhanging limestone cap which juts out over the softer clay beneath.

At the base of the hole is a mixture of boulders and cobbles of both clay and limestone fallen from the cliff above. As you move away from the cliff the seabed is increasingly dominated by empty slipper limpet shells.

The Hounds is a similar clay and limestone feature at a smaller scale with the cliff face generally about 2m high.